Elimination of foreign antigens (Ags) by T cells (e.g. lysis of virally infected cells by cytotoxic T lymphocytes, CTLs) requires the simultaneous recognition of foreign Ag and a product encoded by the individuals major histocompatibility complex (MHC). The goal is to understand the structural basis for the dual recognition of Ag and MHC products by T cells. Previous studies suggest that the T cell specific AlphaBeta-heterodimer is likely to be involved but progress has been hampered in part by the difficulty in raising antibodies (Abs) against the T cell receptor (TCR) complex. This proposal will address the problem by exploring several strategies for isolating monoclonal Abs specific for determinants on the variable (V) and constant (C) regions of Alpha- and Beta-chains and associated structures (T3 subunits) on mouse CTLs. The approach will combine the advantages of xenogeneic immunizations (e.g. mouse CTLs into rats) and screening methods that are specific for the detection of Abs against AlphaBeta/T3 (and not other structures such as lymphocyte-function-associated Ag, Lyt-2, Thy-1, and H-2). For example, one method will use a sensitive colorimetric assay to detect a CTL-specific serine esterase that is released only when the TCR complex is triggered. TCR-specific Abs will be used for examining: 1) relative affinities of AlphaBeta-receptors on different CTL clones; 2) association of Alpha- and Beta-chains with other subunits, such as a product of the Gamma-gene; 3) ontogeny of expression of Alpha, Beta, and T3; and 4) frequency of expression of particular VAlpha and VBeta subfamilies. If the AlphaBeta-heterodimer recognizes MHC products, it is possible that particular Alpha- and Beta-chains are "selected" during development. In an independent approach, VAlpha and VBeta gene probes derived from allospecific CTLs (in previous studies) will be used in the analysis of polyclonal T cell populations to determine if there are restrictions in the assembly and expression of VAlphaJAlpha and VBetaDBetaJBeta gene segments or in the association of Alpha-and Beta-chains. If restrictions are observed, strains of mice with different MHC backgrounds (BALB/c and BALB.B) will be compared to determine if the MHC influences the selection of particular AlphaBeta combinations.